The aqueous nanoparticle dispersion of this invention can be used to make coatings and films for porous and non-porous substrates, such as papers, non-woven materials, textiles, leather, wood, concrete, masonry, metals, house wrap and other building materials, fibreglass, polymeric articles, personal protective equipment (such as hazardous material protective apparel, including face masks, medical drapes and gowns and firemen's turnout gear) and the like. Applications include papers and non-woven materials, fibrous materials, films, sheets, composites and other articles, inks and decorative and industrial coatings, flock and other adhesives and personal care products such as skin care, hair care and nail care products, livestock and seed applications, and the like.
Any fibrous material can be coated, impregnated or otherwise treated with the compositions according to the invention by methods well known to those skilled in the art, including carpets as well as textiles used in clothing, upholstery, tents, awnings, airbags and the like. Suitable textiles include fabrics, yarns and blends, whether woven, non-woven or knitted and whether natural, synthetic or regenerated. Examples of suitable textiles include cellulose acetate, acrylics, wool, cotton, jute, linen, polyesters, polyamides, regenerated cellulose (i.e., rayon) and the like.
The compositions, depending upon their intended application, may be dispersed in a variety of binders including, but not limited to, vinyl-acrylic, styrene-acrylic, acrylic dispersions, solution acrylics, alkyds (e.g., SOYA, TOFA, sunflower, etc.), polyurethanes dispersed in either water or solvent, etc., hereinafter referred to as “binder media”.
Additionally, the compositions according to the invention can be used as adhesives or to augment or supplement adhesive types well known to those skilled in the art. Thus, in the application discussed above wherein the compositions are used as adhesives or to augment or supplement various known adhesive types, particularly desirable properties can be obtained by varying the type and amount of the aqueous nanoparticles used, along with choosing a complementary binder medium from one or more of those listed above, or by incorporating other binder media that would be well known to those of ordinary skill in this art.
As noted above, coatings containing the compositions according to the invention may optionally be formulated as substantially transparent coatings, i.e., typically referred to as ‘clear coats’, or alternately as coatings that serve a glossing and opacifying function. The clear coating composites produced when the aqueous dispersions are applied and dried, exhibit excellent gloss and clarity. Moreover, so long as the D98 particle size of the substantially dispersed nanoparticles contained in the coating composition is ≤350 nm, preferably ≤300 nm and the D50 is ≤200 nm, preferably ≤150 nm, the coatings obtained will be essentially transparent, provided of course that they are free or essentially free of additional components which would comprise their transparency properties.
For purposes of exemplifying and not limiting, the invention, one useful binder medium for forming, e.g., clear coatings according to the invention are polymers containing ester groups such as, for example, polyesters, polyester-based polyurethanes, polyester-based polyureas and polyester-based polyamides. These various binders, however, have less than desirable water-resistance properties due to the hydrolysis group contained therein.
It has been determined, furthermore, that the water resistant properties of such polyester-based polyurethanes can be remarkably enhanced, without affecting the transparency properties of these materials to any significant degree, by combining with the polymer binder a substantially dispersed nano-particle proton scavenger, such as natural ground calcium carbonate-comprising particles. The resultant coating composition, therefore, which again is described only for exemplifying (and not limiting) the invention, thus constitutes a hydrolytically stable polyurethane nanocomposite comprising a solid polyester-polyurethane polymer binder containing proton-scavenger nanoparticles in a substantially dispersed form. One particular useful example of such a formulation would constitute a colloidally stable aqueous dispersion comprising water, a polyester-polyurethane polymer binder and substantially dispersed proton scavenger nanoparticles such as SMGCC.
In the meaning of the present invention the term “substantially dispersed” means that the nanoparticles are properly dispersed in the aqueous medium in order to prevent settling or syneresis of the nanoparticles. This is usually achieved via the addition of well-known dispersants comprising homo- or copolymer chains. If necessary, the chains may be partially or completely neutralized by cations such as sodium, lithium, magnesium, calcium, potassium or ammonium.
Coatings having the composition of the exemplary formulation described above, therefore, constitute polyurethane compositions which, e.g., have improved hydrolytic stability over prior art polyurethane compositions. As used herein the term polyurethane is used generically to describe polymers including oligomers (e.g., prepolymers) which contain the urethane group, i.e., —O—C(═O)—NH— regardless of how they are made. As is well known, these polyurethanes can contain additional groups such as urea, allophanate, biuret, carbodiimide, oxazolidinyl, isocynurate, uretdione, alcohol, amine, hydrazide, siloxane, silane, ketone, olefin, etc., in addition to the urethane groups.
This invention includes, as noted herein the use of substantially dispersed nanoparticles (referring to the primary crystallites or particles of the proton scavenger and or the aggregates of the proton scavenger) of proton scavenger nanoparticles to enhance the water-resistant (hydrolytic stability) of thermoplastic polyurethanes containing polyester segments within the polyurethane polymer or prepolymer. Thermoplastic polyurethanes are made with the same components as waterborne polyester polyurethanes (polyurethane dispersions in water) immediately below but typically the thermoplastic polyurethanes have substantially less or no water-dispersibility enhancing compound(s). In one embodiment the hydrolytically stable polyurethane is a thermoplastic polyurethane. The technology for making and using thermoplastic polyurethanes are well known and described for example in U.S. Pat. No. 6,777,466 B2 and J. K. Backus et al., “Polyurethanes,” in: Encyclopedia of Polymer Science and Engineering. Vol. 13, H F. Mark et al., Ed, pp. 243-303 (1988), the entire disclosure of which is incorporated herein by reference.
Furthermore, the invention in one embodiment relates to polyester polyurethanes which are derived from aqueous dispersions and which, when dried and cured, produce solid polyester segment containing polyurethane products which are tough and, depending on the other ingredients present (e.g., absence of TiO2 or other pigment), can be a transparent.
Further in accordance with this invention, it has been found that the susceptibility of polyester polyurethanes to degrade through hydrolysis can be essentially completely eliminated by incorporating into the polymer a substantially dispersed nanoparticle (referring to the aggregate and/or the ultimate particles/crystallite) proton scavenger.
Certain materials are known to react with, bind to, or otherwise capture protons, i.e., hydrogen ions, when exposed thereto in solid, liquid and/or gaseous media. Calcium carbonate, is a good example as are the other alkali and earth-alkali metal carbonates, i.e., Li2CO3, BeCO3, MgCO3, SrCO3, BaCO3, and RaCO3. Other examples of carbonates which will scavenge protons include carbonates of Fe(II), Fe(III), Mn(II), Zn, Ag, Hg(I), Hg(II), Cu(II), Pb(II), Bi(III).
Calcium carbonate has the formula CaCO3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is found naturally as the following minerals and rocks: aragonite, calcite, vaterite or (μ-CaCO3), chalk, limestone, marble, travertine. The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g., for food or pharmaceutical use), can be produced from a pure quarried source (usually marble). Ground calcium carbonate (GCC) is produced through mechanical grinding of naturally occurring calcium carbonate rocks: marble, limestone and chalk. GCC in pigment formulations provides good rheology and high brightness at low cost. Alternatively, crude calcium carbonate is calcinated into calcium oxide (quicklime). Water is added to give calcium hydroxide, and carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, known as precipitated calcium carbonate (PCC). This process produces very pure calcium carbonate crystals. The crystals can be tailored to a variety of different shapes and sizes, depending on the specific reaction process used. The three main shapes of PCC crystals are aragonite, rhombohedral, and scalenohedral. Within each crystal type, the PCC process can control mean particle size, size distribution, and surface area. Precipitated calcium carbonate is used as a mineral pigment throughout the world for paper production. It is valued for its high brightness and light scattering characteristics in paper filling and coating applications.
Other examples of inorganic compounds which will scavenge protons include silicates of Ba, Ca, Mg, Al, Cr(III), Fe(II), Fe(III), Mn(II), Zn, Ag, Cu(II), Pb(II); sulfides of Fe(II), Mn(II), Zn, Ag, Hg(I), Hg(II), Cu(II), Pb(II), Bi(III), Sn(II); oxides and hydroxides of the above metals; and hydroxyapatite, which is a naturally occurring mineral form of calcium apatite.
Examples of organic compounds which will scavenge protons include 1,8-bis-(dimethylamino)naphthalene, 1,8-bis(hexamethyltriaminophosphazenyl)naphthalene and 2,6-di-tert-butylpyridine.
Any combination of the above scavenges may be used.
In accordance with this invention, it has been found that these proton scavengers materials form will substantially reduce or even completely eliminate the susceptibility of polyester polyurethanes to degrade though hydrolysis without introducing any significant haze into the polymer, but only if they are incorporated into the polymer in a substantially dispersed nanoparticle and/or high surface area form.
In this regard, nanoparticles are typically obtained commercially in powder or dispersion form, both aqueous and organic. Although the individual/primary (crystallites for CaCO3) particles in these products may be in the nano size range, these particles usually combine into larger agglomerates in which the nanoparticles are relatively closely-packed with one another usually in three dimensions. Therefore, when these nanoparticle powders and dispersions are used to make nanoparticle-containing polymers, the nanoparticles remain in the form of these larger agglomerates. In other words, the nanoparticles are not substantially dispersed in the polymer mass. In accordance with this invention, it has been found that proton scavenger nanoparticles will substantially reduce or even completely eliminate the susceptibility of polyester polyurethanes to degrade though hydrolysis, but only if they are incorporated into the polymer mass ultimately formed in a substantially dispersed and/or high surface area form.
An example of substantially dispersed (but loosely aggregated having a high surface area (e.g. 41 m2/g) arrangement is shown in FIGS. 1A and 1B. The primary nano crystallites of Omya XC-6600-34 from Omya form flocks of various shape and dimensions with a substantial portion of the surface exposed to the matrix they are in. From this perspective, the most effective form of flocculation is a trains or chains of particles. Such an arrangement into relatively large floc particles can introduce some haze to the nanocomposites, but will still be effective in retarding ester hydrolysis because large portion of the nanoparticles surfaces is exposed to the matrix.
In one embodiment where the ultimate particle/crystallite diameter is small, desirably the D50 is less than 1 micron, more desirably less than 500 nm, more desirably less than 100 nm, and preferably less than 50 nm. In a similar embodiment, desirably the D90 is less than 1 micron, more desirably less than 500 nm, more desirably less than 100 nm, and preferably less than 50 nm. In one embodiment, the nitrogen BET surface area is greater than 20 m2/g; more desirably greater than 30 m2/g; still more desirably greater than 35 m2/g and preferably about 40 or more m2/g.
In one embodiment, the particle size of the proton scavenger nanoparticles when in the substantially dispersed form desired by this invention can vary widely, and essentially any particle size in the nanoparticle size range can be used. For the purposes of the present invention, nano particles and substantially dispersed nanoparticles are defined as particles which have at least one of the three dimensions of less than about 250 nm (D90) but will normally be less than about 150 nm. In other embodiments, the mean particle size will be about 100 nm or less (D90), 75 nm or less, or even 50 nm or less. In some embodiments, the particle size may even be as low as 25 nm or less, 10 nm or less, or even 5 nm or less. In general, the mean particle size, D50, of these substantially dispersed nanoparticles may be as large as 250 nm (nanometers) but will normally be less than 100 nm. Substantially dispersed nanoparticles having a mean particle size of about 75 nm or less, more typically 50 nm or less, or even 40 nm or less are interesting. In other embodiments, the mean particle size will be 30 nm or less, 25 nm or less, or even 10 nm or less. In some embodiments, the particle size may even be as low as 5 nm or less, 2 nm or less, or even 1 nm or less.
Particle size is usually characterized by particle size distribution, since all particles in a batch of particles do not have an identical particle size. Thus, in some embodiments of the invention, it is desirable that the nanoparticle batch have a D90 of less than 250 nm (i.e., 90% of volume of the particles in the batch have equivalent diameters less than 250 nm). Nanoparticle batches with D90's of 150 nm or less, 100 nm or less, more typically 75 nm or less, or even 50 nm or less, 25 nm or less, 10 nm or less, or even 5 nm or less are especially interesting.
Of particular interest are nanoparticle batches having D90's of about 100 nm or less, and especially 75 nm or less, or even 50 nm or less, since nanoparticles of this size when substantially dispersed in a polymer matrix become essentially transparent to the naked eye.
The aqueous nanoparticle/polyester-polyurethane dispersions of this invention, both in prepolymer and chain extended form, can be used to make coatings and films for porous and non-porous substrates such as papers, non-woven materials, textiles, leather, wood, concrete, masonry, metals, house wrap and other building materials, fiberglass, polymeric articles, personal protective equipment (such as hazardous material protective apparel, including face masks, medical drapes and gowns, and firemen's turnout gear), and the like. Applications include papers and non-wovens, fibrous materials, films, sheets, composites, and other articles, inks and printing binders, flock and other adhesives, and personal care products such as skin care, hair care, and nail care products, livestock and seed applications, and the like.
Any fibrous material can be coated, impregnated or otherwise treated with the compositions of this invention by methods well known to those skilled in the art, including carpets as well as textiles used in clothing, upholstery, tents, awnings, air bags, and the like. Suitable textiles include fabrics, yarns, and blends, whether woven, non-woven, or knitted, and whether natural, synthetic, or regenerated. Examples of suitable textiles include cellulose acetate, acrylics, wool, cotton, jute, linen, polyesters, polyamides, regenerated cellulose (Rayon), and the like.
Compositions of this invention can also be used to produce articles made of stand-alone films and objects such as personal protective equipment. Examples of protective items include gloves and condoms.
In addition, the compositions of this invention can be used as adhesives or to augment or supplement adhesive types well known to those skilled in the art. For example, particular adhesive properties can be achieved by varying type and amount of isocyanates, type, amount, and molecular weight of polyols, and the amount of poly(alkylene oxide) side chain units.
The polyester-polyurethane nanoparticle composites produced when the aqueous dispersions of this invention are applied and dried, whether or not the polyester-polyurethane is chain extended, exhibit exceptional resistance to degradation by hydrolysis, in particular a resistance to hydrolysis comparable to that of the much more expensive polycarbonate polyurethane resins. Moreover, so long as the D90 particle size of the substantially dispersed nanoparticles used is ≤75 nm, preferably ≤50 nm or even ≤40 nm, the polyurethanes obtained will be essentially transparent, provided of course that they are free or essentially free of other materials which would compromise their transparency properties.
Finally, the principles of the present invention can be applied to other technologies for manufacturing aqueous polyurethane dispersions. For example, this invention can be applied to the technique for manufacturing breathable polyurethane dispersions (i.e. dispersions which form layers of breathable polyurethanes) described in U.S. Pat. No. 6,897,281, as well as to the technique for manufacturing core-shell polyurethane dispersions described in U.S. Published Patent Application No. 20050004306. The disclosures of the above patent and published applications are incorporated herein by reference.
Polyurethanes based on polyester macroglycols are known to be susceptible to hydrolysis. The hydrolytic stability of the improved product is attributed to the presence of a proton scavenger in highly dispersed form having significant surface area (increasing the probability that the proton scavenger will be able to scavenge protonic species before the cause hydrolytic chain scission in the polyester portion of the polyurethane). The polyurethane can be in the form of a film, coating or shaped article. The proton scavenger is preferably an inorganic carbonate salt such as calcium carbonate. If the aggregates of the proton scavenger are small relative to the wavelength of light the polyurethane composition will be substantially transparent to visible light. If the proton scavenger, e.g. calcium carbonate, is comprised of loosely aggregated primary crystallites, that are in the 5-100 nanometer weight average diameter, it will have high surface area (e.g. >40 m2/g) will be effective at scavenging protons.
In order to further exemplify the clear coatings formulated according to the invention, several working examples of such clear coat formulations are provided below. In these examples, the following raw materials were used:    DOW—SG30 Acrylic Latex (binder medium)    Bayhydrol 110—Polyurethane Dispersion (binder medium)    Deionized Water    Various Omya experimental SM-GCC slurries.
In addition, the following analytical and testing procedures were used in carrying out these examples:    Gloss was measured at 20°, 60°, and 75° angles utilizing a Micro TriGloss unit from BYK-Gardner, catalog #4446    Sheen at 85° angle utilizing a Micro TriGloss unit from BYK-Gardner, catalog #4446    Solids Content—total solids were measured by Moisture/Solids Analyzer    Toledo HB 43 (Mettler Toledo Corporation)    pH Measurements—pH readings were taken using pH 510 Meter, a pH meter from BYK-Gardner, Catalog # PH-2643.    Gloss/Haze. The preferred evaluation of haze is visual because perceived haze and clarity are one of the most important properties of coatings and other articles. Haze can also be measured by objective instrumental means. Examples include the method described in ASTM D 1003-07 “Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics”, measurement of gloss at different angles, measurement of L,a,b values, and also other methods described in ASTM Guide E179-96(2003) “Standard Guide for Selection of Geometric Conditions for Measurement of Reflection and Transmission Properties of Materials”, D1455 “Test Method for 60-deg Specular Gloss of Emulsion Floor Polish”, D1746 “Test Method for Transparency of Plastic Sheeting”, D4039 “Test Method for Reflection Haze of High-Gloss Surfaces”, D4061 “Test Method for Retroreflectance of Horizontal Coatings” and D523 “Test Method for Specular Gloss”.
Preparation of a Clear Gloss Coating Containing Calcium Carbonate Nanoparticle Dispersion
In each case an aqueous dispersion of substantially dispersed calcium carbonate nanoparticles was produced by from the following ingredients: